1. Field of the Invention.
This invention relates to a magnetic recording and reproducing apparatus, and more particularly, to a magnetic recording and reproducing apparatus in which video signals and audio signal television signals on a plurality of channels are recorded alternately by superimposing these signals on a recording medium, and thus a television signal of a desired channel can be selectively reproduced from the recording medium.
This invention further relates to a magnetic recording and reproducing apparatus, and more particularly, to a monitor video tape recorder which can also record audio signals over a long period of time for the purpose of crime prevention.
2. Description of the Related Arts
FIG. 12 of the accompanying drawings shows a configuration of a video tape recorder (hereinafter called "VTR") as an example of a conventional magnetic recording and reproducing apparatus.
In FIG. 12, the VTR comprises a rotary drum 10 with a non-illustrated rotary head; a head amplifier 11 for amplifying video signals read by the rotary head; a signal processing circuit 12 for demodulating the video signal amplified by the head amplifier 11; an analog-to-digital converter circuit 13 for converting the analog video signals demodulated by the signal processing circuit 12 into digital signals; a memory circuit 14 for storing an output from the analog-to-digital converter circuit 13; a digital-to-analog converter circuit 15 for converting the digital signals outputted from the memory circuit 14 into analog signals; a video signal output terminal 101 for outputting the analog video signals; a memory control circuit 16 for controlling sampling timings or timings for processing the digital signals for the analog-to-digital converter circuit 13, the memory circuit 14, and the digital-to-analog converter circuit 15; a deck sequence control circuit 17 for controlling the sequence of the whole apparatus; a special reproducing circuit 18 for controlling tape running for special reproduction such as frame hold or slow motion reproduction; a servo control circuit 19 for controlling the rotation speeds of the rotary drum 10 and a capstan motor 22 in response to the outputs from the deck sequence control circuit 17 and the special reproducing circuit 18; a capstan motor drive circuit 20 and a drum motor drive circuit 21 to be controlled by the output from the servo control circuit 19; and a capstan motor 22 to be driven by the output from the capstan motor drive circuit 20. The rotary drum 10 is driven by the output from the drum motor drive circuit 21.
Operation of the conventional VTR will now be described.
A VTR performs a reproducing operation in a mode specified by an operation panel as follows. When a tape cassette as a recording medium is loaded in the VTR, the tape is set at a predetermined position in response to a command from the deck sequence control circuit 17. The servo control circuit 19 is actuated under the control of the deck sequence control circuit 17, driving the capstan drive circuit 20 and drum motor drive circuit 21. Then, the capstan motor 22 and rotary drum 10 are driven so as to be rotated constantly at a predetermined speed.
Video signals, which are read by the video head of the rotary drum 10 whose rotation speed and phase are controlled by the foregoing control mechanisms, are amplified by the head amplifier 11, and are demodulated to video signals from FM signals by the signal processing circuit 12.
The video signals demodulated by the signal processing circuit 12 are outputted to the video terminal 101 as they are, being inputted to a television set as ordinary video signals. Otherwise, the analog video signals are converted temporarily into digital signals by the analog-to-digital converter circuit 13 for reasons to be described later.
The digital video signals from the analog-to-digital converter 13 are stored temporarily in the memory circuit 14 including five 256-kb RAMs, converted into analog signals by the digital-to-analog converter circuit 15, and outputted to the video signal output terminal 101 as analog signals.
Needless to say, the number of bits and memory capacity for analog-to-digital conversion can be determined as desired. To prevent deterioration of image quality, a six-bit analog-to-digital converter, a six-bit digital-to-analog converter and a memory having five 256-kb RAMs are necessary. When the frame memory system is adopted as a recording system, it is known that memory capacity twice as large as that for the field memory system is necessary.
The signals are processed digitally by the memory control circuit 16, which performs sampling with a 14-MHz clock frequency and includes a gate array having 3,000 to 4,000 gates.
Generally speaking, it is not always necessary to operate the analog-to-digital converter circuit 13, memory circuit 14, digital-to-analog converter 15 and memory control circuit 16 during reproduction. They are however used to perform a special reproducing operation such as freeze frame or slow motion reproduction. Drive control by the special reproducing circuit 18 and operation of the memory control circuit 16 recall the contents of the memory circuit 14, thereby offering an excellent still or slow motion image.
Specifically, when stopping the tape from running or having the tape run intermittently, the video signals are stored in the memory circuit 14 serving as a field memory while field-reproducing the video signal, thereby providing a good still or slow motion image.
With the conventional VTR as described above, TV signals for only one channel are recorded at a time. Two VTRs must be used to record TV signals on two channels simultaneously.
In addition, since the memory circuit is used only for still or slow motion operation, demands to use the memory circuit more effectively during reproducing have increased.
There is an intermittent recording type of VTR in which the video signals are sampled so as to be recorded and reproduced intermittently. Such a VTR cannot record audio signals but records only the video signals in frames (or fields) intermittently.
FIGS. 13 to 15 show the conventional VTR for intermittent recording.
In FIG. 13, reference numeral 201 stands for a video signal amplifier for receiving video signals from a TV camera at a high impedance, 202 a video signal reproducing circuit including an FM modulator for modulating the video signals into FM signals, 203 an FM signal amplifier for amplifying the FM signals, 204 a mode selector switch for selecting the recording or reproducing mode, 205 a video signal reproducing circuit including an FM demodulator for demodulating the FM signals detected from a magnetic tape at the time of reproducing, 206 an intermittent drive circuit for feeding the magnetic tape intermittently, 300 a rotary drum having two video heads VR and VL, 301 a magnetic tape running to a predetermined extent around the rotary drum 300, 302 a capstan shaft for feeding the magnetic tape 301, and 303 a pinch roller adapted to rotate together with the capstan shaft 302 with the magnetic tape 301 sandwiched between them.
In operation, upon passing through the video signal amplifier 201, video signal reproducing circuit 202 and FM signal amplifier 203, the video signals are converted into FM signals, and applied to the video heads VR, VL on the rotary drum 300 via the mode selector switch 204.
As shown in FIG. 14(a), TV signals from a TV camera include fields V.sub.0, V.sub.1, . . . V.sub.9, V.sub.10, V.sub.11, V.sub.12, . . . in succession. When these fields are recorded successively on the magnetic tape 301, an existing VTR for intermittent recording and reproducing records the fields for a maximum of only eight hours. If every two fields are recorded intermittently, for example, a VTR can perform recording up to 160 hours (8 hours.times.40/2).
For this purpose, not only the magnetic tape 301 should be fed intermittently but also video tracks to be recorded intermittently on the magnetic tape 301 should be obliquely adjacent to one another in succession as shown in FIG. 15.
Therefore, intermittent drive pulse signals are generated based on vertical synchronizing signals by the intermittent drive circuit 206. The pulse signals are applied to a non-illustrated capstan motor drive circuit, so that the magnetic tape 301 is fed accurately to a predetermined extent by intermittent rotation of the capstan shaft 302 and the pinch roller 303, as shown in FIG. 14(b).
The foregoing operation enables the signals to be written on the magnetic tape 301 by the video heads VR, VL of the rotary drum 300. In an ordinary VTR, since both video heads VR and VL have a narrow head gap of 0.25 .mu.m, recording is performed only on a surface layer of the magnetic tape 301.
During reproduction, the FM signals detected by the video heads VR, VL from the magnetic tape 301 are demodulated by the video signal reproducing circuit 205, thereby producing the video signals.
The foregoing VTR of the intermittent recording and reproducing type is composed so as to have the magnetic tape fed intermittently. Therefore, no audio signal has been recorded, by using a stationary head, on the upper edge (linear audio track) of the magnetic tape since the magnetic tape is on standby for about 0.63 seconds.
When the audio signals are recorded by the VHS-HiFi system of the deep layer recording type in timed relation with intermittent recording of the video signals, the video signals sampled at 1/20 can be read as data while the audio signal sampled at 1/20 cannot be read at all.
With the foregoing VTR, recording of the audio signals has to be sacrificed. Unfortunately such a VTR is inconvenient when it is applied as a monitor unit in a burglar alert system, since no sound (voice) can be recorded.